Molybdenum complexes fluorides

The alkylidyne ligands in the molybdenum complexes 179 were modified by deprotonation at the y -carbon with strong bases and subsequent addition of electrophiles [Eq. (146)]. Complexes 180 were desilylated by treatment with fluoride [Eq. (147)] (48). 

Another type of demasking involves formation of new complexes or other compounds that are more stable than the masked species. For example, boric acid is used to demask fluoride complexes of tin(IV) and molybdenum(VI). Formaldehyde is often used to remove the masking action of cyanide ions by converting the masking agent to a nonreacting species through the reaction ... 

SoHd lubricants ate added to help control high friction characteristics in high speed or heavy-duty appHcations where high temperatures are generated. Molybdenum disulfide [1317-33-5] M0S2, may be used alone or in a complex compound formed by grinding with fine natural graphite, and zinc sulfide [1314-98-3] ZnS. Other compounds include calcium fluoride, cryoHte [15096-52-3] Na AlF, rare-earth oxides, and metal sulfides, eg, iron, antimony, or zinc (see LUBRICATION AND LUBRICANTS). 

Sulphuric acid is not recommended, because sulphate ions have a certain tendency to form complexes with iron(III) ions. Silver, copper, nickel, cobalt, titanium, uranium, molybdenum, mercury (>lgL-1), zinc, cadmium, and bismuth interfere. Mercury(I) and tin(II) salts, if present, should be converted into the mercury(II) and tin(IV) salts, otherwise the colour is destroyed. Phosphates, arsenates, fluorides, oxalates, and tartrates interfere, since they form fairly stable complexes with iron(III) ions the influence of phosphates and arsenates is reduced by the presence of a comparatively high concentration of acid. 

Bradfield and Stickland [40,41] determined molybdenum in plant tissue by its catalytic effect on the liberation of iodine from the reaction between potassium iodide and hydrogen peroxide. The detection limit is 0.003 pg/ml of molybdenum. Interference from iron and tungsten can be overcome by addition of ammonium fluoride, but for the greatest precision and accuracy a preliminary separation of molybdenum as its benzoin a-monoxime complex is recommended. 

More complex ceramic binders have been used, but in general the detailed composition of the binder has not been described. One very complex one consisting basically of molybdenum disulphide in silica, had the composition in Table 11.4. Molybdenum disulphide has also been incorporated in fused-fluoride lubricant coatings to improve their properties at temperatures below 500°C. In tests over 450°C in air the molybdenum disulphide was effective for one test, but was then no longer available because of oxidation. However, such coatings would presumably have useful lives at high temperature in vacuum or inert atmosphere. 

B. Semmens and A. B. Meggy, The reaction of kaolin with fluorides, J. Appl. Chem. 16, 122, 1966. D. L. DuBois, Modification of silicon and carbon electrodes with methacrylamide polymers containing covalently attached molybdenum dinitrogen complexes, Inorg. Chem. 23, 2047, 1984. 

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